This invention relates generally to apparatus and methods used in or with magnetic middle ear hearing systems. The invention particularly relates to magnetic implants and to attachment devices and methods for mounting a magnet in a middle ear of a patient. The invention also particularly relates to test instruments and methods with which to locate or determine the orientation or operability of a magnet implanted in a middle ear.
There are many different reasons why some people have hearing impairment. In general, however, sound entering the outer ear canal does not get transmitted to the inner ear and/or transduced, then sent by auditory nerve. In some instances, this can be solved by amplifying the sound with a hearing aid put in the outer ear canal. In other cases, a device that electrically stimulates the auditory nerve directly needs to be implanted in the cochlea of the inner ear. In still other situations, a middle ear device that creates mechanical vibrations is needed. The present invention pertains to such middle ear devices, and specifically magnetic middle ear devices.
A person's normal middle ear includes a chain of small bones, or ossicles. The malleus, the incus, and the stapes form this chain; and when functioning normally, these ossicles transmit mechanical vibrations from the eardrum, or tympanic membrane, at the end of the outer ear canal to the oval window into the inner ear. When something is wrong in this ossicular chain, however, such transmission does not occur sufficiently to stimulate the cochlea and, therefore, auditory nerve. Alternatively, if transmission is normal but inner ear hair cells are damaged or absent, the auditory nerve is less activated. In both cases, greater amplitude of ossicular movement will correct the hearing deficit.
One general solution to hearing problems caused by middle ear deficiencies is to implant a magnet in the middle ear and to cause the magnet to vibrate in response to environmental sounds. The magnet is connected, for example, such that it provides mechanical vibrations to the oval window, either through an adequately functioning portion of the middle ear's ossicular chain to which the magnet is attached or through an implanted prosthesis carrying the magnet and communicating with the oval window.
A number of middle ear magnet attachment devices have been proposed. Some clip to an ossicle, or part of one; others abut ossicular surfaces. Shortcomings of these include clamping or clipping onto living bone (ossicles) with compromise of oxygen and nutrient delivery, wires attached to transducers adding mechanical loading, attaching probes connected to transducers wherein the probes must fit into holes placed into ossicles, gluing implants to living bone wherein the glue is not compatible with living bone and surface tension forces that seek to hold an implant onto the living epithelium of the round window of the inner ear. Additionally, I am not aware of any type of magnetic middle ear device which includes a narrow, completely closed loop that slides over a portion of the ossicular chain. Thus, there is the need for an attachment device and method, as well as an overall implant, which overcomes these shortcomings.
Regardless of the particular implant or mounting technique used for a middle ear magnet, problems can arise with regard to finding where the magnet is, determining what its particular magnetic orientation is, and checking that it is functional. These are significant at least in systems in which the magnet is remotely driven by an electromagnetic signal generated outside the middle ear. If the implanted magnet is not optimally aligned with an external coil from which the electromagnetic signal propagates, the implanted magnet might not respond adequately. Furthermore, some implanted magnets can become ineffective over time, so they need to be tested to see if they are the point of failure in a system that a patient reports has stopped functioning.
Changes in position and function of implanted magnets can occur from a variety of causes. For example, implant surgeons have different techniques and skills and thus magnet location may vary because of differences in surgeons. As another example, one particular type of attachment device might orient its magnet differently from how another particular type of attachment device orients its magnet even though the magnets are located at the same ossicular position in the respective patients. As a further example, anatomical differences between patients can cause similarly located magnets to be oriented differently relative to an external device (such as an external electromagnetic signal generating unit in the person's outer ear canal). Changes in orientation can also occur during the healing process following the implantation surgery (e.g., tissue growth touching the implant can alter its position). Still another example of change is that the functionality of an implanted magnet can deteriorate over time or as a result of leakage in the housing in which the magnet is typically located.
One significant consequence of location or orientation differences has to do with an audiologist's work related to the overall hearing assist system of the type in which an electromagnetic signal is generated and transmitted from outside the middle ear. Occasionally the unit that generates and transmits the signal is one molded to fit in the patient's outer ear canal. The audiologist makes the molded unit. If the audiologist does not know the location or orientation of the implanted magnet, typically the audiologist goes through an iterative process in which several molded units have to be made until the one that causes the implanted magnet to vibrate adequately is obtained. This is expensive, time consuming, and bothersome to the patient. Thus, there is the need for a test instrument and method with which to determine the location or orientation of the implanted magnet.
Another situation an audiologist can encounter is a patient who complains that a previously working system is no longer working. One component that could be malfunctioning is the implanted magnet. It could have become disoriented or dislodged, or its housing could have leaked such that the magnet does not function anymore. The magnet should not decay spontaneously, but it will decay if the housing leaks to body fluids. Such fluids will cause corrosion and the corroded magnet will lose its magnetism. Thus, there is the need for a test instrument and method with which to determine the operability of the implanted magnet.